Balloon-based Atmospheric Investigations of Venus

The VEXAG Roadmap¹ supplemented by two community workshops on the science return, complexities, and risks of aerial platforms² has validated the use of a long-lived, altitude-varying balloon-borne instrumented "aerobot" for the detailed exploration of Venus's atmosphere. Utilizing the large (~80 m s^-1) zonal winds predominate at < 60^o latitude, the aerobot mission concept would circle the planet more than a dozen times over a notional 90-Earth-day science phase as it likely wanders poleward from its deployment near 10^o lat, with an excellent chance of visiting high latitudes >50^o. Onboard instrumentation would sample the environment over all times of day including (1) its winds in all three dimensions, (2) the pressure/temperature structure, and (3) the composition of the air and aerosols³, including (A) UV-absorbing materials which possibly are linked to astrobiology, (B) the reactive sulfur-cycle gases creating the aerosols, and (C) the noble gases, their isotopes and the isotopes of light gases - key to understanding the formation and evolution of the planet and its atmosphere⁴. The aerobot, capable of multiple 10-km-altitude traverses centered near 55-km (~0.5 bar, 25C), would enable 3-dimensional maps of these environmental characteristics as well as the dynamically/chemically influenced size distribution of aerosol particles via a nephelometer/particle-counter⁵ . These traverses also reveal the vertically-varying characteristics of atmospheric stability, gravity and planetary waves and Hadley cells, important for understanding the mechanisms that power and sustain the planet's strong super-rotation. Such altitude excursions also enable measurements of radiative balance and solar energy deposition via a Net Flux Radiometer⁶, another key to understanding super-rotation.

¹VEXAG, 2014. https://www.lpi.usra.edu/vexag/reports/Roadmap-140617.pdf

²Cutts, J. A., et al. 2018. Aerial platforms for the scientific exploration of Venus JPL D-102569.

³ Baines, K. H. et al. 2018. LPI Contrib. #2137. https://www.hou.usra.edu /meetings/vexag2018/pdf/8031.pdf

⁴ Baines, K. H., et al., 2013. In Comparative Climatology of Terrestrial Planets (U. of Ariz. Press, Pp. 137-160.

⁵Renard, J-B. et al. 2016. Atmos. Meas. Tech., 9, 1721-1742.

⁶ Aslam, S., et al. EPSC Abstracts, Vol 10. EPSC2015-388.